I have an issue with a remote user.  I have blocked all outside address 
from SMTP except a spam filtering server to avoid "drive-by-spam".  This 
has worked great except one of the owners uses a Windows Mobile device 
to retrieve and send mail.  The retrieval works great, but Verizon has a 
huge range of addresses that are not contiguous.  I have been able to 
map out ranges as she gets blocked, but this is time consuming and 
frustrating for the client.  Verizon cannot give me a list of ranges 
(I'm not sure if any one person knows them), but can tell me that they 
all resolve to *.myvzw.com.  So far I have no been able to allow access 
based on the host name.  Any suggestion?  I would love to roll these out 
to more clients, but this is going to be a common issue as many clients 
have seen my use my phone for my office email and love the idea.